The invention relates to a vehicle seat having a seat face element, in particular such an element which is equipped with a pressure-sensitive seat occupation sensor system, and a backrest element which can be adjusted between a backrest function position and a lowered position resting on the seat face element.
DE 42 37 072 C1 discloses a vehicle seat having a seat face element which is equipped with a pressure-sensitive seat occupation sensor system in the form of a resistive membrane-type pressure sensor. If the seat face element is loaded, the electrical resistance of the membrane-type pressure sensor which is contained within it changes, and a seat occupation information item is made available and can be fed, for example, to an airbag activation system.
DE 44 09 971 C2 discloses a vehicle seat with a seat occupation sensor system for a seat face element of said seat, which sensor system is capable of detecting the effects of pressure on the seat face element and additionally then deciding whether or not said effects are caused by a child""s seat which has been positioned on said seat. In addition to a pressure sensor element, this vehicle seat has, for this purpose, a base antenna in the seat face element, which base antenna emits an electromagnetic measuring field. The child""s seat is provided with an identification carrier which, within a certain range, brings about a characteristic change, for example attenuation, of the measuring field emitted by the base antenna. In order to sense such a change, the base antenna is assigned an evaluation unit. The evaluation unit can be connected, for example, to an airbag control unit in order to make the airbag control dependent on the occupation of the vehicle seat by a child""s seat.
A seat occupation sensor system for a vehicle seat which is specifically capable of detecting when a child""s seat is positioned on said seat is also described in U.S. Pat. No. 5,618,056. Here, apart from a pressure sensor element in the seat face element, two electromagnetic coils with an associated electronic evaluation circuit are provided. The electromagnetic coupling between the coils is determined by means of the evaluation circuit, the one coil of which functioning as a transmit coil and the other as a receiver coil. In order to detect a child""s seat and possibly its installation direction, said seat has one or more electromagnetic resonators. If the child""s seat is installed on the vehicle seat, the resonator modulates the electromagnetic coupling between the coils in the seat face element. The evaluation circuit is capable of sensing this modulation. Not only a seat occupation information item but also a child""s seat detection information item can thus be fed to a connected airbag activation system.
In vehicle seats having a backrest element which can be folded over into a lowered position resting on a seat face element in order, for example, to be used as a table, the problem arises that when the backrest element is folded over into the lowered position a seat occupation sensor which is contained in the seat can be loaded and it may then possibly feed an incorrect seat occupation signal to an airbag activation system.
The object of the invention is to provide a vehicle seat of the type mentioned at the beginning in which it can automatically be detected in a reliable way whether the backrest element is in its lowered position, and in which as a result no malfunctions occur, such as an undesired activation of an airbag as a result of the triggering of a seat occupation sensor system.
This object is achieved by means of a vehicle seat in which a backrest position sensor system is provided which detects whether the backrest element assumes the lowered position, and in this case outputs a lowered position information item. This lowered position information item can then be taken into account in a suitable way by connected functional units.
In this way it is possible, for example, to avoid unnecessary activation of active restraining means of a vehicle occupant restraining system in a vehicle seat.
In a further development of the invention, the backrest position sensor system is formed by a transponder arrangement with specific encoding and range. In this way, a backrest element position sensor system is created which is easy to mount and at the same time reliable and comfortable.